How to add items to an android layout?

Question

In my main activity I want to add additional TextView items to the layout. I am using the following piece of code in my MainActivity-createOn (partly based on this post and this answer):

LayoutInflater inflater = (LayoutInflater)getLayoutInflater();
View view = inflater.inflate(R.layout.activity_main, null);
GridLayout item = (GridLayout ) view.findViewById(R.id.main_grid);

final int N = 10; // total number of textviews to add

final TextView[] myTextViews = new TextView[N]; // create an empty array;

for (int i = 0; i < N; i++) {
    // create a new textview
    final TextView rowTextView = new TextView(this);
    // set some properties of rowTextView or something
    rowTextView.setText("This is row #" + i);

    // add the textview to the linearlayout
    item.addView(rowTextView);

    // save a reference to the textview for later
    myTextViews[i] = rowTextView;
}
setContentView(view);

The layout for the main activity is as follows:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity" >

    <android.support.design.widget.AppBarLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"/>

    </android.support.design.widget.AppBarLayout>

    <GridLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/main_grid"

        android:useDefaultMargins="true"
        android:alignmentMode="alignBounds"
        android:columnOrderPreserved="false"

        android:columnCount="4"
        >

        <TextView
            android:text="MainTitle"
            android:textSize="32dip"
            android:layout_columnSpan="4"
            android:layout_gravity="center_horizontal"
            android:id="@+id/textView1"
            />


        <TextView
            android:text="Email address:"

            android:layout_gravity="right"
            />

        <EditText
            android:ems="10"
            />

        <TextView
            android:text="Password:"

            android:layout_column="0"
            android:layout_gravity="right"
            />

        <EditText
            android:ems="8"
            />

        <Space
            android:layout_row="4"
            android:layout_column="0"
            android:layout_columnSpan="3"
            android:layout_gravity="fill"
            />

        <Button
            android:text="Next"
            android:id="@+id/imageButton1"
            android:layout_row="5"
            android:layout_column="3"
            />
    </GridLayout>

</android.support.design.widget.CoordinatorLayout>

When running the code, however, no items are added to the main layout. I do not see any other items.

In the end, I want to dynamically add items in a grid layout (columns and rows), which might contain text and icons, and which are clickable (i.e. I can click on an element in this grid-view/layout/whatever, to start a specific action. Maybe this is important information...)

Answer 1

In general, if you want to add items dynamically to a layout at runtime, you can do it as follows (I have substituted your GridLayout for a LinearLayout because I have never used a GridLayout before and am unaware if it requires special layout parameters).

res/layout/activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity" >

    <android.support.design.widget.AppBarLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"/>

    </android.support.design.widget.AppBarLayout>

    <LinearLayout
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:id="@+id/main_grid">

        ... existing views...

    </LinearLayout>

</android.support.design.widget.CoordinatorLayout>

onCreate:

setContentView(R.layout.activity_main);
// `ViewGroup container` is a field
container = (ViewGroup) findViewById(R.id.main_grid); 

anywhere after setContentView:

// `this` would be your activity/application context so it has correct theme info
LayoutInflater inflater = LayoutInflater.from(this); 
TextView[] myTextViews = new TextView[NUMBER_OF_TEXTVIEWS];

for (int i = 0; i < NUMBER_OF_TEXTVIEWS; i++) {
    TextView textView = createNewTextViewWithText("This is row #" + i);

    ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(
        ViewGroup.LayoutParams.MATCH_PARENT,
        ViewGroup.LayoutParams.WRAP_CONTENT
    );      

    container.addView(textView, params);

    myTextViews[i] = textView;
}

createNewTextViewWithText(String text):

private TextView createNewTextViewWithText(String text) {
    // I prefer inflating the TextView, as it's easier to
    // specify layout params in XML, IMO
    TextView textView = new TextView(this);
    textView.setText(text);
    return textView;
}

The layout params are important because it tells the ViewGroup how to add the child (the TextView).